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V . M A N I P U L A T I O N
O F E A C H E L E I V ] E N T
6 ) U s e o f F i e l d D i a p h r a g m
The fie d diaphragm s used for determlning lhe i um nated area on
the spec men The s ze of the dlaphragm is adlusted by manip! at ng
t h e f e d d a p h r a g m c o n t r o r n g . S t o p p i n q d o w n t h e d i a p h r a q m t o
such an extent that the circqrfglelcc qtlh€ lllulll q
circumscribes or inscribes that oJ the evepiece field ol y!€tq s
recommended for genefal microscopy f a w der area than requ red
s l u m i n a t e d , e x t r a n e o u s l L g h t w
l e n t e f t h e f e d o f v e w , c a u s n g f l a f e
n the image and owerng the coftrast Therefore, especaly n
pholom crography, the proper adl!rstrnent of the {eld d aphragm s
very lmpofiant Generaly, good resu ts w ll be achleved when the
d aphragm s stopped down io such an extentthatthe d ameterofthe
luminated area is s ightly afger than the d agonal of the f m format
7 ) U s e o f C o n d e n s e r A p e r t u r e D i a p h r a g m
The condenser aperlure dlaphragm is provided for adjust ng the
fumerica ape{Lrfe (N A.)of the !l !m nating system oi lhe
, - . , -
t 6 . . T m n e 5 e r e o . , o
, . i "
i m a g e . c o n t r a s l , d e p t h o f f o c u s . a n d b r g h t n e s s .
Stopp ng down the aped!re diaphragm w ll ower the resolut on and
b f g h t n e s s b L r t n c r e a s e t h e c o n t r a s t a n d d e p t h o f l o c u s . I n g e n e r a .
when lt is stopped down to 70% to 80% of the numerical ape4llq
of the obiective, a good lmage of appropf ate contrast w I be
obtained (F g. l 1 )
To adlLrst the s ze of the condensef aperture d aphragm, man pu ate
t h e d a p h r a g m c o n t r o r i n g r e i e r r n g t o t h c c o n d e n s e r ' s N . A . s c a e .
o r a f t e r r e m o v n g t h e e y e p i e c e l f o m
t h e e y e p e c e t u b e , a d l ! s t t h e s z e
of the d aphfagm, observ ng the image of the diaphragm that s
vis b e of the br ght c fcle of the ex l pupilon the ins de ofthe objective
Slopping down the apenure diaphragm too tar w I o\/er the
reso v ng power Therefore, it ls recommended not lo slop down the
aperture to a s ze sma ler than 60% of lhe N A oftheobjectve n
, 6
6 , 6 0
. h o ,
o o o , .
g o r - l o
1 1
Size oithe condenser aperture diephr.gm
20
F i 9